The subject matter disclosed herein relates to the art of mechanical fasteners and, more particularly, to an anchor stud for attaching objects or structures to a base material.
An anchor stud is typically used to attach objects or structures to a base material. A typical anchor stud includes a stud, a tapered mandrel or wedge and a clip or sleeve portion. In use, a hole having a diameter that is only slightly larger than the wedge and the sleeve is drilled or otherwise formed in the base material. The size of the hole allows passage of the wedge and the sleeve, while still providing some measure of friction. That is, once inserted into the hole, a nut is rotated onto the anchor stud causing the wedge to be drawn into the sleeve. As the wedge moves along an axis of the hole, the sleeve expands into contact with side portions of the hole. Upon expansion of the sleeve, however, the material thickness of the sleeve is interposed between the wedge and the base material. This effectively increases the diameter of the wedge by roughly twice the thickness of the sleeve. Since the hole diameter in the base material does not change appreciably due to the expansion input, the anchor stud becomes substantially permanently anchored in the base material.
Both function and longevity of such anchor stud rely, in large part, on the properties of the sleeve portion. More specifically the material forming the sleeve must be durable enough to provide suitable anchoring capability and reasonable life particularly in concrete structures that, during their service life, are subject to cracking. Heretofore, the only material deemed acceptable by the art for concrete structures subject to cracking has been stainless steel. While this material is quite appropriate for the task its cost factor is difficult to absorb. Since economic considerations are important in nearly all industries, the art is always receptive to alternative configurations.
In addition to cost considerations, components made of dissimilar metals will, over time when exposed to the elements, experience degradation caused by galvanic corrosion. The galvanic corrosion typically occurs at contact points or interface zones between the components. In addition, stress corrosion cracking will occur as a result of a combination of mechanical loading and chemical attack. More specifically, stress corrosion cracking results from a particular material condition, particular (specific) attacking media, and tensile stresses. When used in concrete, which typically includes calcium chloride, sulfite, aluminum chloride, and other chemicals, mechanical fasteners made from stainless steel are prone to stress corrosion cracking. Stress corrosion cracking is exacerbated on highly cold worked stainless steel. Such cracking is hard to detect on exposed parts and is all but impossible to detect when used in a hole drilled in concrete.